This invention relates in general to drive train systems for transferring rotational power from an engine to the driven wheels of a vehicle. In particular, this invention relates to an improved method for forming a driveshaft tube for use in such a vehicle drive train system.
In most land vehicles in use today, a drive train system is provided for transmitting power from a source of rotational power, such as an internal combustion or diesel engine, to a plurality of driven wheels of the vehicle. A typical drive train system includes a clutch, a transmission, a driveshaft assembly, and an axle assembly which are connected in series between the engine and the driven wheels of the vehicle. The clutch is connected to the output shaft of the engine for selectively providing a driving connection therethrough to the input shaft of the transmission. The transmission provides a plurality of gear ratios between the input shaft and an output shaft connected to the forward end of the driveshaft assembly. The driveshaft assembly is elongated so as to transmit the rotational power from the transmission to the vicinity of the driven wheels of the vehicle. The axle assembly includes an input shaft that is connected to the rearward end of the driveshaft assembly, a differential gear mechanism that is rotatably driven by the input shaft, and a pair of output axle shafts that connect the differential gear mechanism to the driven wheels of the vehicle.
Usually, the output shaft of the transmission and the input shaft of the axle assembly are not co-axially aligned with one another. To accommodate this, a typical driveshaft assembly includes an elongated driveshaft tube having a pair of universal joints secured to the ends thereof. The first universal joint is connected to the output shaft of the transmission, while the second universal joint is connected to the input shaft of the axle assembly. The universal joints provide a rotational driving connection from the output shaft of the transmission through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment therebetween. Thus, it can be seen that the weight of the driveshaft assembly is supported at its forward end by the output shaft of the transmission and at its rearward end by the input shaft of the axle assembly.
Traditionally, driveshaft tubes have been formed from steel alloys having a constant diameter throughout the entire length thereof. Steel alloys are relatively high strength materials. Thus, for a given torque load requirement in a vehicle, a steel alloy driveshaft tube can be formed having a relatively small diameter. For example, in many light trucks and similar vehicles, conventional steel alloy driveshaft tubes have been formed having a diameter of approximately three to three and one-half inches. Unfortunately, steel alloys are also relatively heavy materials. As mentioned above, the weight of the driveshaft assembly is supported at its forward end by the output shaft of the transmission and at its rearward end by the input shaft of the axle assembly. Thus, care must be taken to insure that the weight of the driveshaft assembly can be adequately supported by the transmission bearings that rotatably support the output shaft of the transmission and the axle bearings that rotatably support the input shaft of the axle assembly.
In some vehicles, the distance between the output shaft of the transmission and the input shaft of the axle assembly is relatively small. In those vehicles, the weight of a single elongated driveshaft tube formed from a steel alloy material can be adequately carried by the transmission and axle bearings. However, in other vehicles, the distance between the output shaft of the transmission and the input shaft of the axle is relatively large. It has been found that the weight of a single elongated driveshaft tube formed from a steel alloy material places an undesirably large load on the transmission and axle bearings. In those instances, it is known to split a single elongated driveshaft tube formed from a steel alloy material into a pair of relatively short driveshaft tube sections that are themselves connected together by a third universal joint. A center bearing assembly is provided to support the weight of the interior ends of the two driveshaft sections on the frame of the vehicle, while allowing relative rotation thereof. This structure has been found to sufficiently reduce the amount of weight placed upon the transmission and axle bearings to an acceptable level. However, this structure adds undesirable cost and complexity to the structure and installation of the driveshaft assembly.
Recently, there has been a movement to form driveshaft tubes from alloys of aluminum, as opposed to steel. Aluminum alloys are both strong and lightweight and, therefore, are usually regarding as desirable substitutes for steel alloys in driveshaft tubes. Thus, the weight of a single elongated driveshaft tube formed from an aluminum alloy material is much lighter that a comparably sized driveshaft tube formed from a steel alloy material. Accordingly, a single elongated driveshaft tube formed from an aluminum alloy material can be used in lieu of a split driveshaft assembly structure formed from a steel alloy material (including the third universal joint and center bearing assembly discussed above) without placing an undesirably large load on the transmission and axle bearings.
However, it has been found that an aluminum alloy driveshaft tube having a diameter that is comparable to the diameter of a corresponding steel alloy driveshaft tube tends to vibrate when the vehicle is driven at normal operating speeds. Such vibrations are undesirable because they generate noise. To address this, it has been found desirable to form aluminum alloy driveshaft tubes having a diameter that is somewhat larger than the diameter of a corresponding conventional steel driveshaft tube. For example, in a vehicle drive train system including a steel alloy driveshaft tube having a diameter of approximately three to three and one-half inches, it has been found acceptable to substitute an aluminum alloy driveshaft tube having a diameter of approximately five inches. The larger diameter aluminum alloy driveshaft tube does not vibrate when the vehicle is driven at normal operating speeds.
In some vehicles, the physical space allocated for the driveshaft assembly is sufficiently large to permit the preferred enlarged diameter aluminum alloy driveshaft tubes to be substituted for the conventional steel driveshaft tubes without any modifications to the vehicle itself. Unfortunately, in other vehicles, it has been found that the enlarged physical space occupied by the preferred enlarged diameter aluminum alloy driveshaft tubes causes clearance issues with respect to other components of the vehicle. Obviously, it would be quite time consuming and expensive to modify the structures of such vehicles to accommodate the enlarged physical space occupied by the preferred enlarged diameter aluminum alloy driveshaft tubes. Thus, it would be desirable to provide an improved method for forming an enlarged diameter aluminum alloy driveshaft tube that avoids clearance issues with respect to other components of the vehicle.